Cells, Tissues, Organs and Systems
Cells are the building blocks of life. Most animals and plants are made up of thousands of cells. A cell is the smallest unit of life.
There are basically two types of cells:
Plant Cells & Animal Cells
Cells are alive. They do everything that living things do to stay alive. Cells have different parts to do all these functions.
Below is a picture that shows all the parts of an animal and plant cell.
A cell consists of a mass of living matter called protoplasm. It includes the cell surface membrane, the nucleus and the cytoplasm, where numerous reactions take place.
The nucleus consists of a small spherical mass of denser protoplasm, the nucleolus, surrounded by a membrane called the nuclear envelope. It is embedded within the cytoplasm of the cell and controls the normal cell activities. Within the cells, there are a network of long thread-like structures called the chromatin, spherical structures called the nucleoli and a nuclear envelope.
The chromatin threads contain hereditary materials, i.e. materials inherited from the parents.
The nucleolus plays a part in building up of proteins.
A nuclear envelope separates the nuclear content from the surrounding cytoplasm.
Responsible for cell production
Nucleus is needed for the continued life of the cell, as well as for the repair of worn-out parts.
The part of the protoplasm surrounding the nucleus is called the cytoplasm. It usually forms the larger part of the cell and is the place where most life processes occur.
It usually forms the larger part of the cell and is the place where most life processes occur. The part of the protoplasm surrounding the nucleus is called the cytoplasm.
Embedded in the cytoplasm are some important organelles:
Chloroplast (for plants only)
Cytoplasm - Mitochondria
Involved in the release of energy from food substances during cell respiration
Small spherical or rod-shaped
Cytoplasm – Chloroplast (Plants only)
Sites where plants make their food
Combine together carbon dioxide and water, and using the energy from sunlight to make sugar (glucose)
Cytoplasm - Vacuoles
A vacuole is a fluid-filled space enclosed by a membrane
Animal cells may have many small vacuoles but they are usually not permanent. Vacuoles may contain water and food substances
A plant cell usually has a large central vacuole which contains a liquid called cell sap. Cell sap contains dissolved substances such as sugar, mineral salts and amino acids. This large vacuole is enclosed by a membrane called the tonoplast
Cytoplasm – Cell membrane
The cytoplasm is surrounded externally by a cell membrane (also known as plasma membrane).
It is a partially permeable membrane which controls substances entering or leaving the cell.
Similar membranes may also surround large spaces or vacuoles within the cell.
Cytoplasm – Cell wall (Only in plant cells)
In a plant cell, there is a cell wall which encloses the whole cell.
This cell wall is made of cellulose. It protects the cell from injury.
Cytoplasm – Ribosome
Smallest organelles in the protoplasm
Produces protein from a set of genetic instructions.
Floats freely in the cytoplasm.
Similarities between a plant and animal cell:
Both plants and animals cells have the following structures:
Cell membrane
Differences between a plant and animal cell:
Animal cells usually have many vacuoles while the plant cells only has one large one in the cell
Animal cells does not has chloroplast but a plant cell has chloroplast
Animal cells does not have a cell wall but a plant cell has
Animal cells has its cell filled mostly with cytoplasm while a plant cell only has a thin lining of cytoplasm
Differences between cells, tissues, organs, etc:
Many cells will make up a Tissue
Many tissues working together will make an Organ
Many organs working together will form an Organ system
Many organ systems will form an Organism
What is a tissue?
A tissue is a group of cells which have a common origin and a similar structure, which enables them to perform a particular function.
Tissues in Plants:
Some examples of plant tissues:
Epidermal tissue (also known as epidermis)
Xylem tissue
Phloem tissue
Photosynthetic tissue (also known as mesophyll)
Palisade tissue
Epidermal Tissue
Also known as epidermis
Protects the underlying cells of a leaf by preventing water loss and acts as a barrier to fungi and other invaders.
Xylem Tissue
Transports water and dissolved mineral salts to the leaf.
Phloem Tissue
Phloem transports the manufactured food away from the leaf to other part of the plants.
Photosynthetic Tissue
Also known as Mesophyll
Carries out photosynthesis
Tissues in Animal:
Some examples of animal tissues:
Epithelial tissues
Muscle tissues
Connective tissues
Nerves tissue
Glandular tissue
Epithelial Tissue
Also known as epithelium
This is a sheet of cells which covers the internal and external surfaces of an organ.
This tissue lines both the outside (skin) and the inside cavities of an animal.
Functions include secretion, absorption, protections, trancellular transport, and sense of touch.
Muscle Tissue
Divided into 3 main groups
  1. Smooth muscle tissue
Smooth muscle controls slow, involuntary movements such as the contraction of the smooth muscle tissue in the walls of the stomach and intestines.
  1. Skeletal muscle tissue
Skeletal muscles function in pairs to bring about the co-ordinate movements of the limb, trunk, jaws, eyeballs, etc.
  1. Cardiac muscle tissue
Cardiac muscle tissue plays the most important role in the contraction of the atria and ventricles of the heart.
Connective Tissue
Divided into 4 main groups
Ø Dense connective tissue
It forms ligaments and tendons. It is densely packed and has great tensile strength.
Ø Loose connective tissue
Holds organs in place
Ø Reticular connective tissue
This is a network of reticular fibers (fine collagen) that form a soft skeleton to support the lymphoid organs (lymph nodes, bone marrow and spleen).
Ø Adipose tissue
Used for cushioning, thermal insulation and energy storage.
Ø Nerve Tissue
Make up the nervous system that carries information within the body.
Ø Glandular Tissue
It forms gland that produces substances to secrete hormones or sweat.
Organs of Plant
What is an organ?
An organ is a structure made up of different tissues working together for a specific function.
Organs in Plants:
Some examples of plant organs:
Ø An organ of photosynthesis (contains photosynthetic tissues).
Ø Contains Xylem and phloem tissues and supporting tissues
Ø Provide support and transport food to other parts of the plants.
Ø Contain xylem and phloem tissues.
Ø These tissues take in the nutrients from the roots and transport them to other parts of the plant.
Ø Roots serve to anchor the plants to the soil and absorb water and minerals.
Organs in Animals:
Some examples of animal organs:
Ø Consist of glandular tissues which secrete digestive juices to digest food
Ø Muscle tissue which causes stomach to contract and relax and mix the food well with the digestive juices
Ø Connective tissue which helps to connect the other tissues.
Ø Circulates blood around the body
Ø Consist of blood tissue
Ø Muscle tissue which causes heart to contract and expand to circulate blood
Ø Connective tissue which helps to connect the other tissues.
Organ System
What is an organ system?
An organ system consists of several organs working together to perform a special function, e.g. the digestive system.
Organ systems in Human:
Respiratory system
Ø Lungs, windpipe and mouth.
Ø Supplies the body with oxygen and remove carbon dioxide.
Ø Allows animal to breathe in order to carry out respiration.
Digestive system
Ø Breaks down food into smaller and soluble substances that can be absorbed by the blood.
Circulatory system
Ø Made up of heart, capillaries, arteries and veins.
Ø Allows animal to circulate blood around the body so that different parts of the body will receive food, oxygen, etc in order to work.
With that, I have come to the end of introducing cells, tissues, organs and systems


After learning about cells, tissues, organs and systems, I feel that I have really gained a lot more knowledge about the plant's and the human body's system. During primary school, we were only taught very basic stuff. However, during this lesson, we not only went through most of what we had learnt before, we still learnt more and gained more knowledge on that particular topic. I really like this topic as I feel that the body parts or both animals and plant are really very amazing and I feel that it is very cool being able to learn about it.